The present invention relates generally to medical devices and, more particularly, to a composite knee joint assembly for minimizing or eliminating the production of wear debris resulting from relative motion at the interface between the endoskeleton and tibial tray portions of a composite knee joint assembly.
Knee surgery for the replacement and repair of a patient""s knee has become relatively commonplace in recent years. Prosthetic knee joint devices are available from a variety of manufacturers. Such prosthetic systems, when properly installed, approximate a patient""s natural knee movement.
Typical knee joint prostheses contain a femoral component and a tibial component. The femoral component typically has a generally concave surface portion for fixation and load transfer to the femur, with one or two convex condyles to allow articulation, restrict dislocation or sublixation, and transfer loads to the tibial component. Typical tibial components may be of unitary construction having a bearing surface to articulate with the femoral condyles, and a fixation surface to attach to the tibia by the use of grout, mechanical fixation or biological fixation. The tibial component may also be modular, containing a bearing insert portion and a backing platform portion, or tibial tray, for receiving the bearing insert portion and for affixation on a surgically prepared tibial plateau.
Currently available modular tibial components use a polymeric material for the bearing insert. Such currently available modular tibial components suffer from a tendency toward relative motion between the bearing insert portion and tibial tray. Such relative motion can cause wear in the generation of small particles from the polymeric bearing insert. Such wear can lead to failure of the knee joint prosthesis.
Various attempts to solve this problem include elaborate and often costly locking systems to minimize relative motion at the interface between the bearing insert and the metal tibial tray. In addition, such attempts at solving this problem have often not been modular and therefore have lost the advantages of modularity, including the possibility of interchangability of the bearing insert during surgery and the use of a screw to fix the tibial tray to surgically prepared tibial condyles.
Accordingly, there is a need for modular total knee joint prostheses and unicondylar knee joint prostheses which minimize or eliminate the production of wear debris resulting from relative motion at the interface between the polymer insert and metal tibial tray of knee joint prostheses.
The present invention fulfills the aforementioned need by providing a composite bearing insert for a total knee joint which minimizes or eliminates the production of wear debris that results from relative motion at the interface between the endoskeleton and the metal tibial tray of a total knee joint prosthesis.
In one embodiment of the present invention, a composite bearing assembly for a knee joint is provided, which includes a femoral component and a tibial component, wherein the tibial component includes a metal tibial element and a composite bearing insert structure attached to the metal tibial element. The composite bearing insert structure includes a polymeric bearing component interlocked with a metal endoskeletal component. The endoskeletal component is interlocked with the metal tibial element to minimize or eliminate the production of wear debris therebetween.
The composite bearing assembly may be configured such that the bearing insert contacts the tibial element, such as a tibial tray, only through metal-to-metal contact. In one embodiment of the invention, the polymer insert and tibial tray are interlocked through one or more interlocking dovetails. In various other embodiments of the invention, the tibial tray and bearing insert are interlocked through an interlocking screw arrangement.
The present invention also includes a technique for constructing composite bearing assemblies for total knee joints. In one embodiment of the present invention, the method includes (1) constructing an endoskeleton with a locking mechanism, (2) molding a polymeric powder to form and lock a polymeric bearing element to the metal endoskeleton, and (3) locking the endoskeleton to a tibial tray. In various embodiments of the invention, the locking mechanisms may include interlocking dovetails, a locking taper and/or an interlocking screw arrangement.
The details of the various embodiments of the present invention are set forth in the accompanying drawings and description below. Numerous additional features and advantages will become apparent from a review of the following details of various embodiments of the present invention.